This invention relates to semiconductor devices and, more particularly, to an improved self-aligned aluminum-to-gate member contact in the area of the underlying gate oxide.
It has been found, in certain instances, that one may advantageously increase the packing density of an integrated circuit if the contact is made directly to the gate member in the area directly over the thin gate oxide. However, it has long been realized that a high failure rate exists when an aluminum or other contact is made to a polycrystalline silicon (polysilicon) gate member in the area directly over the thin gate oxide. One theory which may explain this failure mechanism is that after depositing the polysilicon gate member, any subsequent doping of the polysilicon with phosphorus using oxychloride (POCl.sub.3), to produce a conductive polysilicon gate member, enhances grain growth in the polysilicon layer and thus initiates intergrain voids therein. Once the voids have been created, subsequent heat treatments or annealing steps which may occur, for example, during padoxide growth or during subsequent source and drain reoxidation steps, tend to extend the growth of the polysilicon grains and thus both increase the formation and the severity of the voids. As a result, when hydrofluoric (HF) acid is used in a subsequent processing step to remove any oxide that may either be undesired or in direct contact with the polysilicon layer, the underlying oxide is attacked by the HF through the voids created in the polysilicon layer. Thus, any subsequent gate metallization, in the area directly over the thin gate oxide, will result in a short circuit between the metallization and the substrate.